1. Field of the Invention
The present invention relates to an optical fiber, and, more particularly to an optical fiber and an optical fiber ribbon for optical wiring in equipment, ribbon and an optical interconnection system using the optical fiber or the optical fiber ribbon.
2. Description of the Related Art
There are two types of signal transmission in equipment, electrical transmission and optical interconnection. The electrical transmission has a problem with electrical crosstalk due to high density wiring as well as recent high CPU clock speed, thereby requiring specific applications such as reshaping. As a result, the electrical transmission, when used as a signal transmission in equipment, allows a transmission range of at most 100 meters and a transmission rate of at most 10 Gbps. On the other hand, the optical interconnection, when used as a signal transmission in equipment, allows extreme broadband transmission as compared with the electrical transmission, and can provide a signal transmission system using optical elements with small size and low power consumption. Therefore, the optical interconnection system now draws attention as a signal transmission in equipment replacing the electrical transmission.
The optical interconnection uses, for example, optical waveguide circuits or optical fibers, to transmit optical signals. Since it is preferable that all the optical elements used in equipment occupy as little space as possible, the optical fiber, which allows flexible wiring and low loss optical transmission, is especially an optical element suitable for the optical interconnection.
Conventionally, multimode fibers (MMFs) have been used for short-range optical transmission. A conventional MMF fiber has a core diameter about ten times that of a singlemode fiber (SMF), in other words, its numerical aperture is sufficiently large. Accordingly, the MMF fiber does not require an accurate connection between the fiber and other optical element such as a light source, thereby allowing an easy connection. In an optical transmission system using such an MMF fiber, a vertically cavity surface emitting laser (VCSEL) with an emission wavelength of 850 nanometers and a graded index optical fiber are widely used as a light source and an optical transmission medium, respectively. The graded index optical fiber, which is a type of multimode fiber, has a core with an optimal formation of refractive index profile to mitigate the impact of mode dispersion. The graded index optical fiber in which the formation of refractive index profile is accurately controlled allows high-speed optical communication at about a transmission rate of 10 Gbps and over a range of about 100 meters.
However, for further long range transmission or further high speed transmission, application of a broadband SMF is being examined. As a light source used for such application, a GaInAs/GaAs laser diode is now being studied. This laser diode has an emission wavelength of 1100 to 1200 nanometers, a low lasing threshold, and excellent temperature characteristics, may be directly modulated at 10 Gbps, and is therefore drawing attention as a light source for local area network (LAN), for example. Since the emission wavelength can be controlled, so far one with an emission wavelength of 1100 nanometer and one with 1200 nanometers are being studying and are presented at an academic conference and the like.
For example, a transmission system through SMF fibers using GaInAs/GaAs quantum well lasers as a light source is disclosed in Gain F. Koyama et al., 1.2 μm highly strained GaInAs/GaAs quantum well lasers for single-mode fibre datalink, ELECTRONICS LETTERS, Vol. 35, No. 13, pp. 1079-1081, June, 1999 and F. Koyama et al., Data Transmission Over Single-Mode Fiber by Using 1.2 μm Uncooled GaInAs/GaAs Laser for Gb/s Local Area Network, PHOTONICS TECHNOLOGY LETTERS, Vol. 12, No. 2, pp. 125-127, February, 2000. The use of a SMF fiber allows high speed optical communication with a transmission rate of about 40 Gbps.
Consequently, the realization of an optical fiber that has a low bending loss and a low splicing loss, allows high-speed optical transmission, and is suitable for building an optical interconnection system, is desired. Moreover, the realization of an optical fiber that has a small bending diameter in laying and a low failure rate in bending, and that its slack can be stored, is desired.